Incremental position signal transmitters are known, in which a rotatable circular disk has at its edge a track of radial lines scanned by photoelectric light barrier. The pulses obtained with a rotary motion of the disk are applied to a counter, the count of which provides a measure for the position of the disk. In order to obtain a directional signal, two traces with lines are provided, which are angularly offset by a quarter period and are scanned separately. Additionally, a reference mark is also scanned which provides a zero pulse, which resets the counter to zero. In order to achieve, on one hand, high resolution which requires a very fine division while obtaining, on the other hand, a useable change of light current providing a clean pulse, a stationary ruled grating of the same division is provided over the track with the lines. A light beam of finite cross section passes through the stationary ruled grating and the trace with the lines. The intensity of the light is alternatingly a maximum or a minimum, depending upon whether the lines of the trace overlap those of the ruled grating or are separated therewith (DE-AS 1 153 909, DE-A1-33 27849, DE-C2-20 02 583, EP-A2-0 184 628, EP-A2-0222 136).
In conventional position transmitters of this type the movable code element is scanned by light barriers. These light barriers provide electrical signals transmitted through electrical signal lines. Several signal lines are required for several signals. Such electrical signal lines are susceptible to trouble. In particular, electrical signal lines may be influenced by electromagnetic fields.
It is known to transmit optical signals in light piping fibers. The transmission of signals in light piping fibers offers the advantage that the optical signal transmission cannot be disturbed by external electromagnetic fields. It is also known to transmit several optical signals simultaneously in such a light piping fiber. In this case, the signals must be marked, for example, by different wavelengths of the light used for the signal transmission. This is expensive and cannot be effected in some applications.
Code disks are known, which comprise a pattern of dark opaque and of light transparent surface portions on several tracks, each track being scanned by a scanning head. The signals of the scanning heads then provide a digital value representing the angular position of the code disk. According to the prior art, such codings are also photoelectrically scanned by light barriers and transmitted as electrical signals for further processing. In this case a plurality of light barriers and a corresponding number of electrical signal lines are required.